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Structural Innovation and Application Analysis of Electronic Weighing Apparatus at Home and Abroad

 

1. Overview

The load carrier, load cell, and weighing instrument are the three basic components of electronic weighing instruments. The scientific and reasonable structure of the load carrier is an important guarantee for the accuracy, stability and reliability of electronic weighing instruments. In today’s increasingly internationalized electronic weighing market, the improvement and innovation of electronic weighing structures must be guided by user needs and market competition, and will be strongly driven by new technologies, new materials, and new processes. Since the beginning of the 21st century, with the advancement of science and technology and the improvement of industrial process automation and intelligence, various industries have put forward many new requirements for the structure, function and performance of electronic weighing instruments used. Among them, the most important requirement for load-bearing devices is small size. Modularization, light-weight, modularization and integration. If the design of electronic weighing instruments is to develop in the direction of traditional load-bearing devices, load cells, force-bearing components, positioning and limiting devices and other component assembly structures, not only can it not meet the new needs of users, but its own development will also increase. The more difficult it is. On the basis of the existing carrier structure, in order to improve technical performance and meet certain new requirements of users, some small improvements are needed, which can only be achieved at a relatively high price. As the German weighing instrument experts commented in the 1990s, “the structural design of this component-assembled load-bearing device has almost come to an end”. Because the component assembly type carrier structure generally has shortcomings such as tall and heavy, many parts, many moving links, long installation and debugging time, poor stability and reliability, 2 low production efficiency and high cost. Therefore, German weighing instrument experts put forward: “When designing the carrier structure, try to break away from the constraints of the traditional structure and boldly seek another development direction, that is, to reduce size, reduce parts, and save space, which is conducive to achieving optimal production. , Improve efficiency, reduce costs and other directions.” Based on this understanding, some electronic weighing instrument manufacturing companies at home and abroad have carried out a lot of research work on the carrier structure. Their common research and development direction and innovation are the variable component assembly type carrier structure, which is modular, partially integrated and integrated. Carrier structure. It has successively developed modular electronic truck scales and small modular assembly electronic truck scales that are easy to transport; partially integrated electronic truck scales and electronic crane scales with integrated force transmission and positioning and limit devices; integrated weighing rail dynamic electronics Track scale, integrated shearing, curved plate type dynamic road vehicle axle load scale, integrated electronic weighing ring; hollow closed section thin-walled steel structure electronic weighing beam, “bamboo row” thin-walled steel structure electronic platform scale; special purpose The carrier is retractable electronic scale, split-type rolling round-bundle paper electronic scale, etc.

1. Modular electronic weighing instrument
2. Modular electronic truck scale As early as the 1990s, METTLER TOLEDO (Changzhou) Weighing Equipment System Co., Ltd. first realized the design and production of modular electronic truck scale in China. The designer applied the orthotropic bridge design theory to the design of the modular load-bearing device, and appropriately simplified it. The longitudinal beam and the main beam were combined into one to become a closed structure of “U” steel. The bottom beam is simplified into an end plate, and the overlap between the modules and the transition support of the load cell are completed on the end plate. The entire load-bearing module is only composed of “U”-shaped steel, panels and end plates. The so-called modular load carrier is to design and manufacture several standard modular loaders according to the length and rated carrying capacity of trucks and trailers. According to the user’s requirements for the size of the loaders, two or more modules can be arbitrarily overlapped. Compose electronic truck scales of various specifications. For example, according to the length of the truck ≤12m, the length of the tractor and semi-trailer ≤16m, and the length of the trailer ≤20m, the unit length series of the modular carrier are 5m, 6m and 7m, and the preferred width series are 3m and 3.3m. Each series of single, 2, 3, and 4 modules of different widths and lengths can be combined into 22 sizes of load carriers with a length of 5 to 28 m, and more than a dozen commonly used carrier lengths can be selected from them Just as the preferred standard series. This modular electronic truck scale not only enhances the versatility and interchangeability of products, but also greatly improves production efficiency and product quality, and is particularly suitable for large-scale and automated production. 2. The carrier is a small module assembled electronic truck scale. The modularization, standardization and serialization of the electronic truck scale carrier structure is not only conducive to large-scale and automated production, but also easy to move and transport. The American FIRST Weighing Apparatus Manufacturing Company has developed a large-scale electronic automobile scale with a small module assembly type carrier. The difference from the modular electronic truck scale is that the former has a single-section load-bearing module as a whole structure, while the latter is a square. The single-section load-bearing module is divided into two for easy transportation, and it is assembled by two small modules in parallel. According to different size requirements, the single-segment modules connected in parallel are connected in series to form the load-bearing device of the electronic truck scale. The connection between the small modules is through the anastomosing of several supporting feet with sufficient strength on the module and then tightening with screws. Generally, the small load-bearing module is made of 4 “U”-shaped steel or channel steel as the longitudinal main beam, 5 series support legs are welded to the end beam, one positioning support plate, and parallel support legs are welded to the side main beam. Due to the different forces, the structure of the two legs is different.

 

3. Modular industrial axle load scale In order to meet the needs of industrial and mining enterprises for material transfer and internal settlement, the American SI/Allegany company has developed a modular industrial axle load scale that can weigh the axle load and axle group weight of different models, and then give the weight of the entire vehicle. The width of the carrier is the same as that of the integrated weighing board, which is 1.5 times the width of the dual tires (about 750mm), and the length is the sum of the length of the vehicle’s three shafts and the driving distance of the vehicle during the sampling time of the weighing instrument, generally about 1600mm . The modular bearing plates of different lengths are selected to overlap the box-segment weighing beam installed with the cantilever beam load cell to form an industrial axle load scale that can weigh axle weight, axle group weight and vehicle weight. Because the modular axle load scale carrier is longer, in order to make it have sufficient rigidity and low external dimensions, the structure of two modular load-bearing plates lapped on the low-profile box-segment weighing beam is often used in the design. , The modular load-bearing plate is a patterned steel plate reinforced with ribs, and the inclined approach bridges connected to both ends of the load-bearing device are also welded by the patterned steel plate. Figure 2 shows the schematic diagram of the modular industrial axle load scale of the American SI/Allegany Company. The characteristics of this modular industrial axle load scale are: simple structure, low height, light weight, easy to install and carry; load-bearing template and weighing beam overlap, less movable links, high rigidity, and high weighing accuracy; load-bearing template, Box-segment weighing beams and inclined approach bridges can be designed according to modular design, and can be standardized and serialized.

 

III. Integrated electronic weighing instrument

1. Integrated weighing rails In the 1980s, some electronic measurement companies and electronic weighing instrument manufacturers in Europe and the United States were able to meet the requirements of railway transportation, iron and steel metallurgy, coal power plants, port terminals and other departments for the weighing, overloading, underloading, and deviation of materials and transshipment goods. Load inspection, braking force measurement and other needs, developed a weighing rail (Weigh Rail), that is, remove a small section of the rail and paste a resistance strain gauge on it, so that the load cell and the rail carrier are integrated, with dynamic electronics The function of the rail scale achieves the purpose of fast weighing. The integrated curved weighing rail invented by the American engineer Ned Sneed is the most representative. After in-depth analysis of the rail stress and deformation mechanism between the two sleepers, he found that four pieces of uniaxial resistance were attached to the bottom of the rail in the weighing section. Strain gauge, when the wheel passes, the total output of the four resistance strain gauges is equal to the sum of the output of the inner 2 pieces of resistance strain gauge minus the sum of the output of the outer 2 pieces of resistance strain gauge, that is, when the wheel travels through the rail weighing section , The total output of 4 pieces of resistance strain gauge is a constant, as long as this output value is measured, the load capacity of the vehicle can be accurately converted. Although the weighing rail can be cold-welded or connected to the line by a fish plate, which reduces vehicle vibration and improves weighing accuracy, the weighing section has a larger span and greater deflection, which makes it safer. reduce. The bottom surface of the rail can only be polished and cannot be processed, so the output sensitivity of the curved weighing rail is relatively low. Taking the wheel weight of 15t as an example, the sensitivity is only 0.25mV/V. Since the 1990s, the research of integrated weighing rail dynamic electronic railroad scale has developed into a shear-type structure on the basis of a curved structure. It is directly processed on the web of a section of rail that is exactly the same as the line rail, and the strain area is basically the same as that of the double-shear beam type load cell, and the double-shear resistance strain gauge is pasted in the blind hole, which is completely weighed. The sensor manufacturing process carries out wiring, bridge assembly, circuit compensation, protection and sealing, and performance testing, so that this section of rail is integrated with the load cell to form a shear type weighing rail. The American KILO-WATE company, the German PFISTER company, and the GTM company all have a 1.8m-long shear type weighing rail, and the weighing accuracy is better than 0.5. Mechanics model and shear force diagram of shear type weighing rail

 

The mechanical model and shear force diagram of the weighing rail my country’s Beijing Aobangda Technology Development Center, in view of the lack of only one weighing section for the 1.8m weighing rail, has developed a 7.5m long weighing rail dynamic electronic rail scale after theoretical analysis and repeated trials. The original mathematical model of single-axis, dual-axis, and multi-axis weighing and measurement based on the digital summation method overcomes the error caused by the weight transfer between the axles during the driving process of the vehicle. Change the single-axis measurement to 6-axis measurement, and appropriately extend the effective single-axis measurement length, and also use cold welding technology or use fishplates to connect with the lines at both ends to realize the integration of the rail and the load cell to form a continuous rail dynamic Electronic rail scale, its dynamic weighing accuracy is better than 0.5 level. Weighing rail dynamic electronic rail scales generally come with a static self-calibration device, which is convenient for initial installation or in-use inspection. The static self-calibration device uses the self-balancing principle of the gantry structure, and realizes the loading of the symmetrical heavy rail at all levels through the hydraulic loading system and the standard load cell installed on the gantry. The structure of the static self-calibration device of the weighing rail electronic railway scale.

 

2. Integrated weighing board As early as the late 1960s, the American Association of State Highway Workers (AASHO) put forward a “four-time method” of vehicle axle load damage to road pavement through experimental research, where: D-relative to the standard Load, the destructive effect coefficient of the actual axle load of the vehicle on the highway; W—the actual axle load of the vehicle; W0—the standard axle load of the vehicle. For example, the standard axle load mass designed for an expressway is W0=10t, and the vehicle runs according to this standard, that is, W=W0=10t, then D=1, which has no destructive effect on the highway. When the actual axle load mass of the vehicle W=12t, D=2.0736; when W=16t, D=6.5536. When the actual axle load mass of the vehicle doubles, that is, when W=20t, D=16, it can be seen that when the axle load mass of the road vehicle exceeds the limit, the seriousness of the damage to the road is shown. Therefore, every country in the world restricts and inspects the axle load quality of vehicles running on highways. For this reason, all countries in the world control and manage highway vehicle axle load exceeding limits by restricting axle load. my country, the United Kingdom, Germany, the Netherlands, and Brazil Other countries limit the standard axle load of road vehicles to 10t, while France, Spain, Iran and other countries limit the standard axle load to 13t. This equipment for detecting the quality of vehicle axle load is a road vehicle dynamic axle load scale. At present, the integrated structure weighing board (Weighpad) type axle load scale is widely used in countries all over the world. American Amcells Company, Intercomp Company, British Trevor Deakin, German Mikros Systems Company, GTM Company, Pfister Company, Canadian Mass Load Company, etc. have successively developed weighing plate-type dynamic axle load scales. The shear type weighing plate of Trevor Deakin Company in the United Kingdom and the curved type weighing plate of PAT Company of Germany are the most representative ones. The structure of the shear type weighing plate and the installation diagram of the curved weighing plate are shown in the figure.

 

 

The structure and installation drawing of the curved weighing plate of German PAT Company The main features of the shear and curved weighing plate axle weighing scale are: (1) The load bearing, support, and load cell are combined into one to form an integrated whole The structure, the shear type weighing plate is made of hard aluminum alloy, and the curved type weighing plate is made of plastic mold steel, which reflects the development direction of the carrier with compact structure, low height and light weight. The general height is about 2.5cm. The weights of the curved weighing plates with dimensions of 175cm×50.8cm×2.3cm and 125cm×50.8cm×2.3cm are 114kg and 81kg respectively; the weight of the duralumin alloy shearing weighing plate is only about 30kg. (2) The shear type and bending type weighing plate itself is a large plate type load cell. The resistance strain gauge, wiring bridge, circuit compensation and adjustment are carried out in accordance with the manufacturing process of the weighing sensor. In order to adapt to the harsher working environment, multi-layer sealing technology is adopted, that is, after the polyurethane potting sealant is implemented in the long blind groove, the entire weighing plate is sealed with vulcanized rubber, which is extremely moisture-proof, waterproof, and salt-fog-proof. Anti-corrosion and anti-freezing ability. (3) By reasonably choosing the position of the resistance strain gauge, wiring the bridge and adjusting the eccentric load, the anti-eccentric load ability of the weighing plate is improved. (4) Because the weighing board is an integrated structure, there are no moving links and mutual friction parts, and it has strong anti-vibration and impact capabilities, reducing the dynamic components composed of various harmonics during dynamic measurement, and has high working reliability and stability. it is good. 3. Integrated weighing hook The integrated weighing hook electronic crane scale combines the rings, scale body, load cell and hook of the traditional electronic crane scale into one to form an integral structure. That is, at both ends of the single-shear beam type load cell, anti-symmetric hoist rings and hooks are respectively processed to make it a larger S-type load cell, which is called a weighing hook abroad. Its force form and measurement performance are exactly the same as ordinary S-type load cell. The dedicated miniaturized weighing display control instrument, wireless transmitting device and antenna are installed on the side of the circuit compensation and adjustment box of the weighing hook. By controlling the anti-symmetric ring and hook ruler to 8 inches, the balance of the hook body and the weighing display control instrument can be realized. The roots of the rings and hooks, that is, the ends of the shear beam load cell, should have sufficient rigidity to ensure that the strain zone is in a pure shear stress state.

 

The characteristics of the weighing hook electronic crane scale are: compact structure, small size, low height, light weight, easy to install and carry; the hoisting ring, the hook and the load cell are an integral structure, which can be processed with high coaxiality Grade, load concentricity is good, eccentricity error is small; the weighing hook itself is a complete weighing sensor, without other activities, high weighing accuracy and good stability. 4. Integrated weighing ring The integrated weighing ring-type electronic crane scale is basically the same as the weighing hook. It also combines the hanging ring, scale body, weighing sensor and hook of the traditional electronic crane scale into one to form an overall structure . The difference is that the weighing ring uses a bridge-type double-shear beam type load cell, and the double-shear beam type load cell and the hook form a closed loop. Compared with the weighing hook, the rigidity of the hook is increased, the structure is more symmetrical and reasonable, and the accuracy and stability of the measurement are improved. The disadvantage is that instead of directly forming the hoisting ring, a hoisting ring hole is formed. A horseshoe ring that bears the pulling load and a pin that bears the shearing force are required to complete the lifting and weighing task. Because the weighing ring itself is a complete double-shear beam weighing sensor, it can be produced in full accordance with the manufacturing process regulations of the weighing sensor, ensuring the accuracy and reliability of weighing

4. Partially integrated electronic weighing instruments Not all electronic weighing instruments’ carriers can be designed as integrated structures. For those electronic weighing instruments with larger carrier sizes or more complex structures, a partially integrated structure design can be adopted. For example, the weighing sensor is integrated with the load-bearing force transmission and positioning and limiting device in the part of the load carrier; the load-bearing support of the load cell is integrated with the load carrier; the load cell is integrated with the electronic crane scale carrying shell. 1. The electronic truck scale integrated with the load cell and the force transmission positioning and limiting device. Since the electronic truck scale must accommodate the entire car and trailer when weighing and measuring, the volume and table size of the load carrier are very large, which is impossible The integrated design of the carrier, support and load cell is integrated like a weighing board. At the connection between the load cell and the load bearing device, a more complicated force-bearing force transmission, positioning and limiting device must be designed to complete the weighing and measurement task. The traditional design methods can be summarized into three main types: One is the use of double-shear beam type load cell top ball support, that is, the 3-inch steel ball on the load cell is used to support the load carrier to transmit the load, and the longitudinal direction of the load carrier must be added. And lateral limit device. The second is a double-spherical rocking pillar assembly that uses automatic centering, force-bearing, force-transmitting, positioning and limiting. Its structure can be regarded as a double-spherical rocking pillar assembly formed by stretching a steel ball. It consists of a double-spherical rocking column and O-shaped rubber. It is composed of sealing ring, cylindrical base and polytetrafluoroethylene board. Through reasonable selection of the spherical radius, the height and diameter of the double-spherical rocking column and other dimensional parameters, the limit clearance of the carrier is controlled to achieve the purpose of limiting the longitudinal and lateral movement of the carrier. The third is the automatic centering force-bearing force transmission limit device integrated with the elastic element of the load cell and the rocker, which combines the elastic element of the load cell and the double-spherical rocker into one, which is designed as a whole structure, namely It is the sensitive component of the load cell, and also plays the role of automatic centering and force-bearing limit of the double-spherical rocker. The disadvantage of the above scheme is that there are many parts, the inconsistency of manufacturing and assembly, and the friction and displacement between the connecting parts can cause nonlinearity and discreteness. It is difficult to ensure the “load force distribution of the load bearing device” during the use of the electronic truck scale. The coefficient” is constant. The best design to solve the above problems is to integrate the load cell and the load-bearing load-bearing load, positioning and limiting device into a single component, which is a partially integrated design for the large load-bearing device. The force-bearing and force-bearing positioning and limiting device of the line contact chain link assembly of Canada’s MASS LOAD and the line-contact saddle ring force-bearing and force-bearing positioning and limiting device of RICE LAKE of the United States are the most representative. When the line-contact chain link assembly or saddle ring assembly is introduced to transfer the load, it can effectively overcome the horizontal force of the carrier, realize automatic balance positioning and limit, and ensure that the “carrier force distribution coefficient” is constant during the use of the electronic truck scale. constant. The former requires a cantilever shear beam structure at both ends of the fixed support in the middle of the load cell. Two linear contact chain links are respectively suspended at the two ends of the double cantilever shear beam. Four load cells and eight chain links support the load-bearing device. , Play the role of force-bearing force transfer positioning and limit; the latter requires fixed supports at both ends of the double-shear beam type load cell, and a line-contact saddle ring is suspended in the middle of the shear beam, and it is connected with the load-bearing device to bear the force The force transmission positioning and limiting function is a single chain link translation and rotation structure, and there is no problem of synchronization of the two links. image

The load-bearing device of the large electronic truck scale integrates the complex force-bearing force transmission, positioning and limiting device and the load cell into a line-contact chain link or saddle ring component through a partially integrated design. Its outstanding features are: (1) Simple and compact structure, reasonable connection with load cell and load carrier, frictionless load transfer, cast steel parts, convenient cold and hot processing, low cost, especially suitable for a large range of electronic truck scales and electronic platform scales; (2 ) The chain link or the saddle ring is a line contact suspension type flexible force transmission method, which has the ability to automatically adjust and adapt to the deformation of the carrier after the load is loaded and the thermal expansion and contraction deformation caused by the temperature change; (3) With the chain link Or the double-shear beam type load cell supporting the saddle ring, its loading point and supporting point are self-balanced force system, the load carrier has a low center of gravity and good stability; (4) In the process of force transmission force positioning and limitation, it has Multi-dimensional degrees of freedom and omni-directional displacement performance ensure that the “load bearing force distribution coefficient” is constant.

 

November 10, 2021